The present disclosure relates to anti-ice systems, and more specifically, to a system for delivering ice protection or anti-ice fluid in an anti-ice system.
Ice buildup on aerodynamic surfaces of aircraft can be problematic. For example, ice can build up on the leading edges of wings and/or engine nacelles. The ice can also disrupt the intended airflow over the aerodynamic surfaces, causing a loss of lift generated by the aerodynamic surface. A combination of design considerations of modern airfoils and modern certification requirements result in less ice tolerance, meaning that modern aircraft need to have more anti-ice capability than some conventional anti-icing technologies can provide. However, existing anti-ice technologies are complicated and/or expensive.
Civil aviation aircraft utilize fluid ice protection systems to anti-ice wing leading edges, windshields, and propellers. Generally, aircraft with on-board anti-ice or de-ice capability use systems selected from bleed air systems, Tecalemit-Kilfrost-Sheepbridge (TKS) systems or Freezing Point Depressant (FPD) systems, and pneumatic/mechanical boots.
FIG. 1 illustrates a bleed air system 100 wherein ice protection is provided by a pneumatic swirl system utilizing hot bleed air inputted 102 into the engine inlet from the engine core. A small percentage of the core mass flow is extracted between compressor stages, and transferred to a ‘D-duct’ formed by the inner surface of the nacelle lip and the upstream surface of the forward bulk-head as shown in FIG. 1. Such systems provide ice protection via thermal flux through the nacelle lipskin and are about 50% efficient, with roughly half of the energy in the high pressure, high temperature bleed air transferred through the metallic lip and about half remaining in the overboard exhaust.
However, the bleed air system has a number of limitations. Firstly, the inlet structure must accommodate high internal temperatures and pressures, which are exacerbated by a variety of failure modes and dispatch considerations. Secondly, the engine idle power setting must be increased when the engine anti-ice (EAI) system is operating, so that bleed flow extraction does not exceed engine capability in this condition. Thirdly, because the power setting must increase when the EAI is on, the maximum thrust available when the EAI system is operating is decreased. Finally, Specific Fuel Consumption (SFC) also increases when the EAI system is operating. Though this has only a small impact on block fuel usage for most missions, it becomes significant when the effect on engine-out conditions analyzed as part of conformance with Extended-range Twin-engine Operational Performance Standards (ETOPS) is considered. Ultimately the SFC increase due to EAI increases the required fuel reserve and impacts take-off weight for every mission. For Ultra High Bypass (UHB) engines with large fan diameters and smaller cores, these issues are magnified. In fact, the reduction in maximum thrust available due to the EAI system may ultimately impact UHB engine core size and result in weight and SFC penalties.
Consequently, FPD systems are considered the most efficient, using a glycol-based fluid that is wept onto the leading edge of an airfoil, an engine nacelle, and/or a spinner for a propeller or fan from a porous panel. The FPD system utilizes Direct Current (DC) motor driven pumps to deliver the anti-icing fluid to the relevant surfaces. The pumps extract fluid from an unpressurized reservoir and boost it to approximately 100 psia. The glycol-based fluid mixes with water droplets, lowering the freezing point of the water droplets so that the water droplets cannot freeze. The mixture of glycol-based fluid and water droplets then flow off the aircraft together.
However, DC pumps have a number of drawbacks. Firstly, while the DC pump reliability is acceptable for civil aircraft operations, a DC pump will likely will not be installed in a friendly environment on a commercial aircraft. For example, low vibration areas will get too cold and high vibration areas may be too hot for proper operation of the DC pump.
In addition, the porous panels in FPD systems leak fluid when not in use and/or when the ambient temperature changes. Warm temperatures reduce the viscosity of the anti-icing fluid causing the anti-icing fluid to leak out of the porous panels. In commercial engines leaking fluid is not acceptable due to foot traffic around the engine while in tarmac.
Moreover, the flight envelope of commercial aircraft may exacerbate leakage. As a result, FPD system components may not be robust enough to certify for commercial aircraft because the system Mean Time Between Failures (MTBF) is not high enough.
What is needed, then, is a solution that reduces power requirements of anti-ice systems, improves delivery of anti-icing fluid, mitigates leakage of the anti-icing fluid, and increases robustness of anti-ice systems using anti-ice fluid. The present disclosure satisfies these needs.